Microsoft announced Monday it has begun the long-expected beta test of the first service pack for Windows Vista. In addition, it has also begun shipping the first release candidate, or RC, of Windows Server 2008, which includes an early version of its upcoming virtualization software.

The company said a month ago that Vista Service Pack 1 (SP1), which has already been in a closely limited beta test since earlier in the summer, would ship to a broader beta audience "in a few weeks."

That is happening now as Microsoft releases the SP1 beta to a list of around 12,000 testers, according to an e-mail from a company spokesperson. The service pack will include all of the various patches and hotfixes that have been released for Vista so far, as well as updated device drivers.

Just as importantly, especially for Microsoft's legal team, it also adds capabilities needed to enable third-party desktop search engines to easily replace Microsoft's own search engine as the default  a promise that the company made last spring to the judge overseeing its U.S. antitrust consent decree.

Windows Vista SP1 is currently scheduled for final delivery in the first quarter of 2008.

Meanwhile, the company is also shipping RC0  Release Candidate Zero  of Windows Server 2008. In Microsoft parlance, the release candidate stage is the last phase between beta test and the final shipping release.

One bonus feature with RC0 is the inclusion of a community technology preview (CTP) of Microsoft's hypervisor-based Windows Server virtualization technology, codenamed Viridian. (For Microsoft, a CTP is a less formal way of releasing code to interested parties for testing without going through an official beta test step.)

"Windows Server 2008 includes a thin (under a megabyte), hypervisor-based software virtualization layer that runs between the hardware and the Windows Server 2008 operating system," according to a Microsoft statement.

While the company has had some basic virtualization products available for several years, namely Virtual PC and Virtual Server, which both run on top of Windows  Microsoft has been vocal about how the arrival next year of its Windows Virtualization technology for Windows Server 2008 will provide so-called "hypervisor" capabilities. The hypervisor enables multiple operating system sessions, each running in its own VM, to run simultaneously on a single physical host.

Viridian is not scheduled to be in Windows Server 2008 when it ships. However, it is scheduled to ship within 180 days of the server's release. In late August, Microsoft disclosed that it has pushed back the final ship date for Windows Server 2008 to the first quarter of next year.

No need to get too excited, however, said one long-time Microsoft observer. The beta of the Vista service pack has been expected and much dissected already, for instance.

"That just means that people who are interested in evaluating [Viridian] can do that testing," he added.

Windows Server 2008, which was previously codenamed Longhorn Server, will provide many new capabilities that it has in common with Vista, including the Aero user interface.

It will also provide important new functions such as "server core"  a minimal installation option that enables an administrator to deploy only what's needed of Windows Server 2008, such as a Web server, sans the graphical user interface, instead providing a command line for management use.

Another key new feature will provide what the company terms Network Access Protection or NAP  which will automatically sequester new PCs on the network until they meet defined levels of security.